1. Field of the Invention
The present invention relates to a gas tank and a method of manufacturing a gas tank liner. More specifically, the present invention relates to an improvement in the structure of a gas tank and a method of manufacturing a suitable liner for the gas tank with the improved structure.
2. Description of the Related Art
A gas tank (high-pressure gas storage container) used for storing or supplying hydrogen and the like is known that includes: a tank body that has a liner in which the outer peripheral surface is impregnated with resin and reinforced with a carbon fiber reinforced plastics (CFRP) layer, for example; and a cap that is made of alloy and attached to the opening of the tank body. For example, a valve assembly (a part that includes a high-pressure valve and the like) may be attached to the cap that is provided in a tank opening.
A gas tank (e.g., a hydrogen storage container) that includes an inner layer and an outer layer is also disclosed in which a gas-venting flow passage that leads to outside the tank is formed between the inner layer and the outer layer (see Japanese Patent Application Publication No. 2004-176885 (JP-A-2004-176885), for example).
However, if the gas-venting flow passage is formed between a contacting surfaces of the two layers (the inner layer and the outer layer) as in the above gas tank, strength of the tank may be compromised.
In order to solve such a problem, the inventors has made various deliberations. In such high-pressure tanks, the problem may be attributed to the two-layer structure that is formed from a liner layer as the inner layer and a fiber reinforced plastics (FRP) layer as the outer layer, as trace amounts of hydrogen gas may permeate through the liner layer when the tank remains under a pressurized state. In this case, because a space between the FRP layer and the cap is pressure-sealed in the highly pressurized tank, hydrogen gas accumulates between the liner layer and the FRP layer, thereby causing inward deformation of the liner layer (see FIG. 11). When the inner pressure of the tank decreases as hydrogen gas is consumed, hydrogen gas that has high concentration leaks from the tank through the weakly sealed space between the FRP layer and the cap (see FIG. 12). After the deliberation on high-pressure tanks, particularly on the phenomenon that hydrogen gas permeates through the liner layer, the inventor has reached a new finding that links to a solution for the problem.